Anterior Lobe

Research has shown that the hormonal activity of the anterior lobe is controlled by chemical messengers traveling from the hypothalamus to the anterior lobe.

In the 1950s, the British neurologist Geoffrey Harris discovered that sectioning of the infundibular stalk, which interrupted the communication between hypothalamus and hypophysis, impaired the function of the hypophysis.

In 1964, chemical agents called releasing factors were found in the hypothalamus; and shown to control the secretion of pituitary hormones.

In 1969 the American endocrinologist Roger Guillemin and colleagues isolated and characterized thyrotropin-releasing factor, which stimulates the secretion of thyroid-stimulating hormone from the pituitary.

In the next few years his group and that of the American physiologist Andrew Victor Schally isolated the luteinizing hormone-releasing factor, which stimulates secretion of both LH and FSH, and somatostatin, which inhibits release of growth hormone. For this work, which proved the connection between brain and the endocrine system, they shared the Nobel Prize in physiology or medicine in 1977.

Human somatostatin was one of the first substances produced for pharmacological use in bacteria by recombinant DNA technology. The presence of the releasing factors in the hypothalamus helped to explain the action of the female sex hormones, estrogen and progesterone, and their synthetic versions contained in oral contraceptives.

Growth | Sexual development | Lactation | Metabolism | Stress

The hypophysis plays an important role in regulating body growth. By releasing growth hormone (GH), the hypophysis promotes lengthening of the bones.

The action of GH is meditated by another hormone called insulin-like growth factor-1 (IGF-1), produced mainly by liver and bones. The growth-promoting effect of GH ends at puberty, when sexual hormones (androgens and estrogens) close the cartilage of linear bones.

But the GH action continues in adulthood. In fact GH has also a relevant role in regulating some metabolic pathways, especially mediating protein usage in skeletal muscles. This is the reason why GH has become one of the most used and dangerous medications for body-builders.

GH also acts on heart muscle, and recent studies have shown that GH replacement therapy improves heart performances in patients with GH deficiencies.

In women, FSH favors the development of one ovarian follicle at each menstrual cycle, and the production of estradiol by the granulosa cells. LH mediates ovulation (departure of the oocyte from the ovarian follicle) and the production of progesterone by the corpus luteum.

The pituitary gland regulates lactation by producing the hormone prolactin. This hormone is responsible for the maintenance of lactation, after the mammary gland has been prepared for milk production by estrogens. During the entire post-partum period prolactin is increased because breast suckling stimulates prolactin production. The high prolactin value is also the reason why women are infertile during this period. In fact, this hormone can inhibit the production of gonadotropins and block follicle maturation in the ovary.

The adenohypophysis exerts an important role in several metabolic pathways. The most important hormone the gland produces is called thyrotropin (TSH).

The main role of TSH is to regulate the synthesis and production of thyroid hormone from the thyroid gland. These peripheral hormones play a basic job in our metabolism. In fact, they are important in catabolism, the mechanism by which our body burns calories and produces heat.

Thyroid hormones are also very important in regulating other physiological actions:

• brain development during fetal period,
• heart function,
• emotional reactions such as anxiety, nervousness or happiness

Finally, they can interfere in the reproductive system by altering menstrual regularity and libido, or in the skeletal system by regulating bone mass.

The hypophysis can regulate some aspects of the stress. Generally, stress can be defined as an emotional and physiological response to a disagreeable situation.

The pituitary is important in some severe and acute stress situations, during which it produces a hormone called ACTH. ACTH stimulates the adrenal cortex, where it regulates the synthesis and production of cortisol. During severe trauma, burns, illness, fever, hypotension, physical exercises, surgery and hypoglycemia, cortisol production increases. Cortisol supports the body's adaptation to the stress condition, by increasing glucose use, the heart activity or electrolyte exchanges.

Finally, ACTH also exerts a less important function in the adrenal cortex: steroid production. In 1975 scientists identified another peptide: endorphin, which acts in experimental animals as a natural pain reliever in times of stress. Endorphin and ACTH are made as parts of a single large protein, which subsequently splits. This may be the body's mechanism for coordinating the physiological activities of two stress-induced hormones. The same large pro-hormone that contains ACTH and endorphin also contains short peptides called melanocyte-stimulating hormones. These substances are analogous to the hormone that regulates pigmentation in fish and amphibians, but in humans they have no known function.

Two hormones are secreted by the posterior lobe. One of these is the antidiuretic hormone (ADH), vasopressin. Vasopressin stimulates the kidney tubules to absorb water from the filtered plasma that passes through the kidneys and thus controls the amount of urine secreted by the kidneys.

The other posterior pituitary hormone is oxytocin, which causes the contraction of the smooth muscles in the uterus, intestines, and blood arterioles. Oxytocin improves the contractions of the uterine muscles during the final stage of pregnancy to stimulate the expulsion of the fetus, and it also stimulates the ejection of milk from the mammary glands following pregnancy.